OPPOSED FORCED FLOW SMOLDERING OF POLYURETHANE FOAM

An experimental study is carried out of the effect on the propagation of a smolder reaction through the interior of a porous fuel of a force d flow of oxidizer opposing the direction of smolder propagation. The potential effect of buoyancy in the process is also analyzed by conduc ting the experiments in the upward and downward propagation, and compa ring the respective results. The experiments are conducted with a high void fraction flexible polyurethane foam as fuel and air as oxidizer, in a geometry that approximately produces a one-dimensional smolder p ropagation. Measurements are performed of the smolder reaction propaga tion velocity and temperature as a function of the location in the sam ple interior, the foam and air initial temperature, the direction of p ropagation, and the air flow velocity. For both downward and upward sm oldering three zones with distinct smolder characteristics are identif ied along the foam sample. An initial zone near the igniter were the s molder process is influenced by heat from the igniter, an intermediate zone where smolder is free from external effects, and a third zone ne ar the sample end that is affected by the external environment. The sm older velocity data are correlated in terms of a nondimensional smolde r velocity derived from a theoretical model of the process previously developed. The analysis of the results confirm that the smolder proces s is controlled by the competition between the supply of oxidizer and the transfer of heat to and from the reaction zone. At low flow veloci ties oxygen depletion is the dominant factor controlling the smolder p rocess, and the smolder velocity and temperatures are relatively small . Increasing the flow velocity strengthens the smolder reaction due to the oxygen addition resulting in increased smolder velocities and tem peratures. These parameters, however, reach a maximum and as the air v elocity is increased further the smolder reaction becomes weaker and e ventually dies out due to convective cooling.